Permanent Freeze

No it’s not Pan’s labyrinth, it’s a HiRISE image of a portion of Mars’ south polar ice cap showing frozen mesas made of layers of carbon dioxide ice. During the winter months on Mars – which is considerably colder than Earth – carbon dioxide is deposited as frost in the upper latitudes and evaporates – well, sublimates – in the spring and summer. But on parts of Mars’ south pole there are places where this “dry ice” does not melt. Instead it builds up over time, creating permanent layers up to 30 feet thick…this is Mars’ “residual” ice cap.

The swirls and organically-shaped features of the residual cap are collectively referred to as “Swiss-cheese terrain”, and are caused by uneven sublimation of the CO2 ice, possibly due to different compositions of the layers beneath. It’s suggested that the flat depressions overlie areas containing harder water ice.

The terrain changes patterns over time, and the HiRISE camera aboard the Mars Reconnaissance Orbiter – along with previous images from the Mars Orbiter Camera – is being used to monitor those changes season to season to learn more about the movement of carbon dioxide in Mars’ atmosphere as well as the surface of the planet beneath the ice. At the same time, we get to be treated to beautiful images like this showing a fascinating physical process in action on another world!

“Knowing the amount and rate of carbon dioxide removal can give us a better idea of the role of carbon dioxide (the main component of the Martian atmosphere) in polar and atmospheric processes, of current environmental and climatic conditions, and of how Mars climate may be changing.”

– Patrick Russell, University of Arizona Department of Planetary Sciences